Early stabilization of body fluid loss can be important in the treatment of wounds and bleeding tissues. For example, many injuries are treatable if effective hemorrhage control and operative surgical intervention are undertaken rapidly. In many situations, however, immediate access to surgical care is not available. Internal wounds and bleeding sites may be particularly difficult to treat in such situations, as traditional treatment techniques (e.g., application of pressure to stop bleeding, etc.) are difficult to implement with such wounds.
Although the use of polymers in the treatment of wounds is well known in the art, previous materials and methods for treating wounds with polymers have suffered from a variety of drawbacks. For example, many polymers irritate skin and/or internal tissues. Moreover, many polymers lack suitable mechanical properties to be useful inside the body; polymers that are too stiff may lead to discomfort or further injury, while polymers that are too soft may fail to provide adequate support for internal tissues. In addition, polymers can be difficult to place within internal wounds or bleeding sites that may have complex shapes and geometries.
One clinical application in which polymers have been used to control bleeding is in the treatment of aneurysms. Generally, an aneurysm is an abnormal widening or ballooning of a portion of a blood vessel due to weakness in the vessel wall. If left untreated, aneurysms can grow large and rupture, causing internal bleeding which is often fatal. Two locations in which aneurysms are commonly found are in the abdominal aorta and the brain.
Abdominal aortic aneurysms (“AAAs”) are conventionally treated by surgical removal or by endovascular repair. If the AAA is surgically repaired, a major incision is made in the abdomen or chest to access and remove and/or repair the aneurysm, and the aneurysmal segment of aorta is replaced or supplemented with a tubular graft of synthetic material such as Polyethylene terephthalate (PETE) or Polytetrafluoroethylene (PTFE). If instead it is treated by endovascular aneurysm repair (“EVAR”), the AAA is accessed via catheter using minimally invasive techniques rather than through an open surgical incision. A graft or stent-graft is delivered through the catheter and self-expands as it is expelled from the catheter to bridge the aneurysm to form a stable channel for blood flow. FIG. 1 shows an aneurysm 110 in an abdominal aorta 115 after treatment by the placement of a stent-graft 150, as is known in the art. With the increased use of EVAR in recent years, a higher incidence of endoleaks has been observed. An endoleak results from blood that is still able to access the aneurysm sac 116 after placement of the graft or stent-graft. Such a leak could be caused by an insufficient seal at the ends of the graft (referred to as a “type I” leak), retrograde flow into the aneurysm from collateral vessels (a “type II” leak), a defect in the graft (a “type III” leak), and flow through any porosity in the graft (a “type IV” leak). Such endoleaks represent a significant possible drawback to EVAR procedures as they could lead to aneurysm expansion or rupture. Endoleaks are less of a concern following surgical repair of AAA, but the surgical procedure is significantly more invasive and has higher mortality and morbidity. Thus, an improved EVAR device and system which address endoleaks would provide a significant improvement in patient care.
It has recently been proposed (Rhee et al., “Treatment of type II endoleaks with a novel polyurethane thrombogenic foam: Induction of endoleak thrombosis and elimination of intra-aneurysmal pressure in the canine model,” J. Vascular Surgery 2005, 42(2): 321-8), incorporated herein by reference, to use a pre-formed polyurethane foam in the aneurysm sac following an EVAR procedure. The authors found that the use of such a foam resulted in a reduction of intra-aneurysmal pressure to a level that was indistinguishable from control aneurysms that had no endoleak. Such a pre-formed foam, however, cannot be shaped in situ to conform to the configuration of the aneurysm sac. As such, the authors were required to make use of numerous foam implants to achieve the reported results.
Likewise, it has been proposed in U.S. Publication No. 2009/0287145, incorporated herein by reference, to introduce a foam material into an aneurysm. The foam is compressible to allow for injection and then expands from its compressed configuration and hardens in situ. The foam itself, however, is pre-formed prior to injection into the aneurysm.